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  • Lin, Jia-Lin, Brian E. Mapes, Klaus M. Weickmann, George N. Kiladis, Siegfried D. Schubert, Max J. Suarez, Julio T. Bacmeister, and Myong-In Lee, 2008: North American monsoon and convectively coupled equatorial waves simulated by IPCC AR4 coupled GCMs. Journal of Climate, 21, 2919-2937.

This study evaluates the fidelity of North American monsoon and associated intraseasonal variability in IPCC AR4 (the Inter-governmental Panel on Climate Change Fourth Assessment Report) coupled general circulation models (GCMs). Twenty years of monthly precipitation from each of the 22 modelsí 20th century climate simulation, together with the available daily precipitation from 14 of them, are analyzed and compared with GPCP monthly and daily precipitation. We focus on the seasonal cycle and horizontal pattern of monsoon precipitation, together with the two dominant intraseasonal modes: the eastward-propagating Madden-Julian oscillation (MJO) and the westward-propagating easterly waves.

The results show that current state-of-the-art GCMs have significant problems and display a wide range of skill in simulating the North American monsoon and associated intraseasonal variability. Most of the models reproduce the monsoon rain belt extending from southeast to northwest. However, most models overestimate the precipitation over the core monsoon region throughout the seasonal cycle. Although many models reproduce the gradual northward shift of precipitation from March to July, several models simulate a nearly simultaneous increase of precipitation in northern and southern latitudes, leading to a too-early monsoon onset. Moreover, most models fail to reproduce the gradual southward shift of precipitation from August to November, and keep the high precipitation in monsoon region until the end of the year.

Regarding the intraseasonal modes, most of the models produce overly weak variances for both the MJO and easterly waves, and simulate poor eastward propagation of the MJO. Nevertheless, most models simulate good westward propagation of easterly waves.


Full Article: http://lightning.sbs.ohio-state.edu/publication.html

Last Updated: 2008-10-23

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